A federal autopsy report on the Michael Brown shooting has confirmed the same findings as previous autopsies by local officials and a private examiner hired by the 18-year-old's family, documents have shown.

The Armed Forces Medical Examiner System's autopsy showed the teen's death was caused by multiple gunshot wounds to the head and chest, but also revealed a minor gunshot wound to Brown's right hand.

Gunshot wounds on the black teen's right hand and "microscopic examinations" showed a "strong likelihood of the presence of soot," indicating a close-range discharge of a firearm, which matched Darren Wilson's account - the white officer who was acquitted last week of his killing - that the pair had a scuffle through the open window of his police car moments before Brown was shot.

"The gunshot wounds of the right chest may represent re-entry wounds from the exiting gunshot wounds to the right arm and/or the right forehead," the report said.

The Associated Press has reviewed all of the grand jury documents that have been released and none appear to include a transcript or a recording of a two-hour FBI and county police interview with Brown's friend, Dorian Johnson, who was with Brown when he was shot.

The shooting death of Brown provoked days of unrest in St Louis, which later spread across the United States and abroad, after a grand jury decision not to indict Wilson.

Wilson resigned from the Ferguson Police Department last month. He told St Louis Dispatch he was resigning of his "own free will" and hoped the community would "heal" following weeks of violence and protests.